Solenoid having a rotatable back stop for the plunger



Jan. 7, 1964 R. s. STONE 7, 7 SOLENOID HAVING A ROTATABLE BACK STOP FORTHE PLUNGER Filed Feb. 2. 1962 FIG. 1

INVHVTOR. Richard 6? Stone BY United States Patent 3,117,257 SQLENOIDHAVING A RDTATABLE BACK STOP FOR THE PLUNGER Richard S. Stone, MountProspect, IlL, assignor to Anderson Controls, Inc., Franklin Park, Ill.,:1 corporation of Illinois Filed Feb. 2, 1962, Ser. No. 170,68

5 Claims. (Cl. 317-186) This invention relates to a novel solenoid,particularly to a solenoid constructed to have means to eliminate orgreatly reduce buzzing when it is actuated with A.C. energy.

The plunger of a solenoid is a magnetic member that moves between twopositions in use. When the actuating coil is energized, the plunger isdrawn into a closed-gap position where it comes to rest against anelement placed to restrain its movement. This element is called abackstop. When the coil is not energized, a restoring force, such as aspring or a hydraulic or pneumatic device, forces the plunger away fromthe backstop into its second position which is limited either by amechanical element that interferes with further movement or simply bythe extent of the means exerting the restoring force.

Solenoids that are actuated by A.C. energy tend to buzz or chatterbecause, as the alternating actuating energy passes through zerovoltage, the magnetic force decays and the restoring force moves theplunger slightly away from the back stop. When the flux is againestablished, the plunger is snapped into contcat with the back stopagain. The collective result of this sequence of events occurring twiceeach cycle is a buzz or chatter.

To avoid this buzz, an annulus of copper, called a shading ring, isembedded into the face of the backstop or sometimes the plunger. Theshading ring is usually positioned to be concentric with the axis of theplunger. The backstop, which forms part of the magnetic circuit of thesolenoid, is made of magnetiza-ble material, and the shading ringbecomes, in effect, a single winding of a transformer of which thebackstop is the core. The alternating magnetic flux produced by the coilof the solenoid acting through the shading ring, changes the phase of aportion of the alternating magnetic flux in the backstop. Thus, when thetwo portions of the flux are out of phase, there will always be magneticflux in the circuit tending to resist the restoring force and therebyholding the plunger in contact with the backstop.

Even in a circuit containing a shading ring as described above, afluctuating or pulsating force is exerted on the plunger. When the faceof the backstop that restrains movement of the plunger is notperpendicular to the axis of the plunger, this pulsating lforce causesthe plunger, which is loosely held in a guide, to tip and hit againstthe guide twice each cycle thereby producing a buzz. If, for example,the guide and backstop are in a C-shaped frame, adjustingperpendicularity by bending the frame is too ditlicult andtime-consuming for mass production, and as a result, buzzing A.C.solenoids are considered inevitable and are simply endured.

Even if the solenoid were produced with the backstop perpendicular tothe axis of the plunger as above described, when the plunger isconnected to do work it may buzz due to its working environment. Forexample, if

the solenoid is installed to do work on a load that is non-axial oreccentric with the plunger, the plunger will tip against the guidestwice each cycle and create a buzz. To avoid buzzing from non-axialmechanical loads, the restraining face of the backstop must beperpendicular to the resultant of the force components of the axialmagnetic force and the non-axial mechanical force. Therefore, a solenoidthat is adjusted to be quiet under no load conditions may buzz wheninstalled for its ultimate use due to the introduction of non-axial loadon the plunger.

This invention provides a novel structure for an A.C. actuated solenoidthat permits the solenoid to be adjusted to tune out a buzz or chatter.The solenoid of this invention contains the usual elements of a solenoidwhich may include a coil, a plunger, a means to exert restoring force, ashading ring, and the elements required to make a magnetic circuit.Additionally, the solenoid of this invention is provided with a backstopthat is formed with the plunger-restraining face non-perpendicular tothe axis of the backstop. The backstop so formed is then rotatablymounted in the usual position in a solenoid, and preferably it ismounted to be difiicultly rotatable so that it will remain in anadjusted position. The backstop may also be provided with adjusting elements such as a slot to receive a screw driver or flats for engagementwith a wrench.

When a newly assembled solenoid constructed in accordance with thisinvention is found to buzz due to lack of perpendicularity between theplunger and the backstop, the backstop can be slowly rotated therebychanging the angle that its plunger-restraining face makes with the axisof the plunger to a position which will compensate for the lack ofperpendicularity.

When a solenoid, installed with its plunger connected to do WOl'k,bnzzes because of non-axial mechanical loads on the plunger, thebackstop again can be slowly rotated to seek a position where therestraining face is perpendicular to the resultant of the Various forcecomponents on the plunger and thereby to tune out the buzz. It has beenfound in practice that a backstop formed with a restraining face at anangle in the order of from about one-half degree to two degrees or morewith a plane perpendicular to its axis will almost always be adjustableto a position of quiet operation. In those few solenoids in which theangle is not properly complementary to compensate for the particularload characteristics or structural characteristics of the solenoids, theorientation of the parts may be quickly changed to create a new set ofconditions for the backstop by such simple means as tapping the frame afew times with a hammer or bending it slightly with a screw driver orpliers. These changes in orientation constitute a rough adjustmentbecause they, in themselves, do not stop buzzing. The changes inorientation just create a new set of conditions or a new environment inwhich the adjustable backstop may work.

The accompanying drawings illustrate a solenoid embodying this inventionand are presented as illustrative of the invention rather than limitingon its scope.

FIG. 1 is an elevation view, that is partly in section and partlyschematic, of a solenoid embodying this invention;

FIG. 2 illustrates a bottom view of the solenoid of FIG. 1;

FIG. 3 is a plan view of the back stop element of the assembly shown inFIG. 1; and

FIG. 4 is a sectional view of FIG. 3 taken along the line 4 4.

The main structural element of the illustrated solenoid is a frame thatsupports most of the elements and maintains proper relative positions.The frame 10 is in the shape of a 0 having a main connecting element 11holding an upper extension or embracing element 12 spaced from a lowerextension or embracing element 13. A coil 15 is embraced between theupper and lower extensions. The coil -15 surrounds 'a guide tube 16which is parallel to the connecting element 11 and extends between theupper extension 12 and the lower extension 13. An opening 17 in theupper extension 12 and another opening 18 in the lower extension '13 arealigned with each other and placed so that they open into opposite endsof guide tube 16.

A plunger 20 rides in the guide tube 16 and extends through the opening17 in the upper extension 12. A contracted portion 21 of the plunger isemployed to hold the small end of a conical compression spring 22, thelarge end of which rests against the upper portion of upper extension12. The spring 22 is the means for supplying a restoring force to theplunger 20.

A backstop 23 is connected within the hole 18 in the lower extension 13.One face of the backstop is a plunger-engaging surface 25 having acopper shading ring 26 embedded in it. The surface '25 lies in a planeat an angle A from the plane perpendicular to the axis of rotation ofthe backstop 23 and it is positioned to form a closed end in the guidetube 16. 'In the drawing, the angle A is exaggerated for purposes ofillustration. The backstop 23 also has a radially contracted portion 2 7and an adjusting portion 28 that protrudes fro-m the hole 18. Theportion 28 is of smaller diameter than hole 18, but of greater diameterthan portion 27. The surface 25 and the main body 24 of the backstop areof greater diameter than hole 18. The adjusting portion 28 is adaptedwith a toolengaging means such as the slot 30 to receive a screw driver.

The assembly of the solenoid of this invention is quite simple. Theguide tube 16 is placed between the upper frame extension 12 and thelower frame extension 13 and fixed in place by the pressure of those twoelements, by lapping the end of the tube, by welding, by brazing or byother conventional means. The coil and guide tube may be a singleintegral unit, for example, as when a coil is potted in plastic with acylindrical opening down the center of the plastic body to act as aguide tube. After the coil and guide tube are assembled, the backstop isintroduced through opening '17 in the upper frame extension and passedthrough the guide tube so that the element 28 extends through the loweropening 18. A spring clip 31 or other holding means that is adapted toengage the indentation 27 and to hold the entire backstop assembly 23 intension, is placed around the indentation 27 thereby preventing thebackstop from coming out of opening 18. The spring clip also causessufficient friction between surface 32 of the main body of the backstop,and inner surface 33 of extension 13 to render backstop 23 difficultlyrotatable. The plunger 20 may then simply be placed in the guide tube sothat the spring 22 engages the upper surface 35 of extension 12 to holdthe plunger in its extended stable position.

To operate the solenoid a source of AC. energy is connected to the coil15 by conventional means which are not shown. When the coil isenergized, the mag netic circuit which includes the plunger 20, theframe 10 and the backstop 23 causes the plunger to retract into theguide tube 16 and to come in contact with the plunger engaging surface25 thereby compressing the spring and doing work on whatever mechanicalelement is connected to its other end, such as a valve stem. For thereasons set forth above, the characteristic buzz from the plunger mayoccur when the coil is energized. 'Ihe backstop 23 is then slowlyrotated to tune the solenoid to a position of no buzz or to a positionof minimum buzz. Of course, if the buzz is tuned out, as is the casewith most solenoids constructed in accordance with this invention, thereis no need for further adjustment. If the buzz is not completely tunedout by rotating the backstop 23, the relative position of extensions 12and 13 may be slightly changed by prying them a bit further apart with ascrew driver or tapping them closer together with a hammer. By thischange of position, a new environment for the backstop 23 is createdwhich will present another opportunity for the backstop to exist in aposition where no buzz will be encountered.

The angle A that the surface 25 forms with a plane perpendicular to theaxis of the backstop will depend upon the details of construction of anyparticular solenoid and to some extent on its intended use. The angle Ais usually a very small angle, in the range from about one-half degreeto about two degrees. However, it is within the scope of this inventionto produce a solenoid that can be tuned for maximum buzzing. A solenoidtunable for maximum buzz is useful, for example, if it is employed tooperate a safety device in which the buzz of the solenoid acts as analarm. For such purposes, the solenoid may not only be tuned for maximumbuzz, but the backstop may be constructed with the angle A larger thanusual to promote as much tilting of the plunger as possible.

Although this invention is described with respect to the particularsolenoid illustrated in the accompanying drawings, it is intended thatthe invention is of general application and is not limited to anyparticular construction.

Having thus described the invention, what is claimed l. A solenoidcomprising a coil having an opening therethrough, said coil maintainedbetween spaced first and second embracing elements, a plunger at leastpartly within said opening, force exerting means connected to urge saidplunger from within the opening in said coil, and a backstop rotatablymounted in said first embracing element to close one end of the openingin said coil and positioned to engage the plunger when it is drawn intothe coil, said backstop having a copper annulus embedded in theplunger-engaging face, said plunger-engaging face lying in a plane thatis not perpendicular to the axis of rotation of said backstop.

2. The solenoid of claim 1 further characterized in that said backstopis held in said first embracing element by resilient means that producesa normal force between contacting surfaces on said backstop and saidfirst embracing element whereby the resultant friction produces adifficultly rotatable connection therebetween and whereby said backstopis substantially immovable longitudinally of the axis of rotation ofsaid backstop.

3. The solenoid of claim 1 further characterized in that theplunger-engaging face of said backstop lies in a plane that is at anangle of from about one-half degree to about two degrees to a planeperpendicular to the axis of rotation of said backstop.

4. The solenoid of claim 1 further characterized in that theplunger-engaging face of said backstop is maintained within the openingin said coil and the other side of said backstop extends through andbeyond said first embracing element, said other side havingtool-engaging means formed thereon.

5. A solenoid comprising a coil having a central opening therein, saidcoil maintained between spaced first and second embracing elements, aplunger guide means axial with the opening in said coil, a plungercoaxial with said guide means and at least partly within the end of saidguide means opposite said first embracing element, force exerting meansconnected to urge said plunger from within said guide means, and abackstop mounted in said first embracing element to be ditficultlyrotatable and positioned with a plunger-engaging face within said guidemeans, said backstop having a copper annulus embedded in theplunger-engaging face, said plunger-engaging -face lying along a planethat is at an angle of from about one-half degree to about two degreesfrom the plane that is perpendicular to the axis of rotation of saidbackstop.

References Cited in the file of this patent UNITED STATES PATENTS

1. A SOLENOID COMPRISING A COIL HAVING AN OPENING THERETHROUGH, SAIDCOIL MAINTAINED BETWEEN SPACED FIRST AND SECOND EMBRACING ELEMENTS, APLUNGER AT LEAST PARTLY WITHIN SAID OPENING, FORCE EXERTING MEANSCONNECTED TO URGE SAID PLUNGER FROM WITHIN THE OPENING IN SAID COIL, ANDA BACKSTOP ROTATABLY MOUNTED IN SAID FIRST EMBRACING ELEMENT TO CLOSEONE END OF THE OPENING IN SAID COIL AND POSITIONED TO ENGAGE THE PLUNGERWHEN IT IS DRAWN INTO THE COIL, SAID BACKSTOP HAVING A COPPER ANNULUSEMBEDDED IN THE PLUNGER-ENGAGING FACE, SAID PLUNGER-ENGAGING FACE LYINGIN A PLANE THAT IS NOT PERPENDICULAR TO THE AXIS OF ROTATION OF SAIDBACKSTOP.